This invention relates generally to lead frames for use in integrated circuits packages. More particularly it relates to a modified lead frame for reducing the likelihood of electrical contact between the bonding wires and leads crossed over by the bonding wire.
As technology advances, the dimensions of integrated circuit packages continues to decrease therefore requiring corresponding decreases in integrated circuit dies. The decrease in the physical size of integrated circuit dies necessitates a similar reduction in the size of lead frames. This coincides with the leads of the lead frame approaching smaller and smaller dimensions (fine lead pitch) which increases the likelihood of electrical contact between bonding wires and other leads of the lead frame. This is especially a problem with lead frames having leads that are arranged in such a fashion that the path of the bonding wire, from the die to the appropriate lead to which it is bonded, crosses over other leads. In a conventional lead frame, as shown FIG. 1, the leads 4 form a radial pattern away from a die 6. The die 6 is wire bonded to leads 4 by bonding wires 8 such that they do not cross any other leads prior to bonding, therefore the aforementioned problem is not an issue. In lead frames where the leads are very small or are closely spaced, then there is an increased likelihood that the bonding wires may contact leads during the wire bonding process. A major factor influencing whether undesired contact will occur is the tolerance and precision of the wire bonding equipment during wire bonding.
There are also situations where undesired contact of bonding wires may result from random factors. By way of example, bonding wire sweep during the injection molding process causes the viscous encapsulating material to move the delicate bonding wires which may, in turn, cause contact with the leads. Them have been a number of methods employed to deal with bonding wire sweep. One successful technique is by using a glob-topping material to form a hardened barrier over the bonding wires prior to injection molding. Another has been to inject the material in such a way that the impact on the bonding wires is minimized, namely, injecting in direction as parallel to the bonding wires as possible. A disadvantage with glob-topping is that it adds additional steps and cost to the manufacturing process. Both methods are preventative type measures taken after a successful bonding process and neither will prevent contact caused by the wire bonding process itself. It is therefore an objective of the present invention to provide a method and apparatus that reduces the likelihood of bonding wire contact with crossed leads that is both simple and cost effective.